|Publication number||US7523848 B2|
|Application number||US 11/148,540|
|Publication date||Apr 28, 2009|
|Filing date||Jun 9, 2005|
|Priority date||Jul 24, 2001|
|Also published as||US20050284914|
|Publication number||11148540, 148540, US 7523848 B2, US 7523848B2, US-B2-7523848, US7523848 B2, US7523848B2|
|Inventors||David T. Beatson, Deepak Sood, Norman Lucas, Zhijie Wang|
|Original Assignee||Kulicke And Soffa Industries, Inc.|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (36), Referenced by (5), Classifications (23), Legal Events (2)|
|External Links: USPTO, USPTO Assignment, Espacenet|
This application claims the benefit of priority to U.S. Provisional Patent Application No. 60/581,575, filed on Jun. 21, 2004, the contents of which are incorporated in this application by reference. This application is a continuation-in-part of U.S. patent application Ser. No. 10/458,535, filed on Jun. 10, 2003 now U.S. Pat. No. 6,997,368 which is a divisional of U.S. patent application Ser. No. 10/131,873, filed on Apr. 25, 2002, issued as U.S. Pat. No. 6,729,530 on May 4, 2004, which is a continuation-in-part of U.S. patent application Ser. No. 09/912,024 filed on Jul. 24, 2001, issued as U.S. Pat. No. 6,412,683 on Jul. 2, 2002.
The invention relates generally to a method and apparatus for measuring the size of free air balls on a wire bonder. More specifically, the present invention relates to the use of a prism such as a cornercube prism to produce the image of a capillary tip with a free air ball present. The present invention is used in conjunction with a machine vision system to analyze the image and measure the diameter of the ball prior to bonding.
The fabrication of electronic assemblies, such as integrated circuit chips, typically involves inspection of the device at various phases of the fabrication process. Such inspection procedures often utilize vision systems or image processing systems (e.g., systems that capture images, digitize them and use a computer to perform image analysis) to guide the fabrication machine for correct placement and/or alignment of components.
In fabricating such electronic assemblies, wire bonding is typically used to interconnect the integrated circuit chip with a lead frame. Other well-known interconnect processes include, for example, ball-bumping and stud-bumping. As part of these bonding processes a bonding ball is formed at the end of the bonding wire using a well-known electric flame-off (EFO) technique. The size (diameter) of the bonding ball (free air ball) depends on the current and duration of the EFO. As wire bonders are used for packaging finer and finer pitch devices, it would be desirable to measure and control free air ball diameters in an effort to regulate ball size for ultra fine pitch application.
A conventional vision system (shown in
Further, in conventional systems, bonding ball diameter is typically measured off-line. That is, the bonding process is interrupted so that the ball diameter or the resultant stud (in the case of stud-bumping) can be measured. Changes in the size of the bonding ball are then made to the EFO system, again off-line, to correct for the size of the bonding ball. Thus, the bonding ball size is measured and adjusted via an off-line calibration sequence and programmed into the wire bonder.
These conventional systems have deficiencies, however, in that they have no way of determining the effect of these settings without again going to an off-line measurement. Thus, the ball size determination and control is open loop and requires interrupting the bonding process, negatively impacting device throughput.
Accordingly, it would be desirable to provide a system and method for allowing a wire bonder to periodically measure the ball diameter so that the EFO system may be controlled to produce the desired size ball continuously without the necessity to interrupt the ball bonding process with off-line measurements and adjustments.
According to an exemplary embodiment of the present invention, a system for measuring the size of free air balls for use with a wire bonder having a wire bonding tool and an Electric Flame Off (EFO) device is provided. The system includes an imager disposed above a first image plane, a prism disposed below the imager, and at least one lens positioned between the first image plane and the prism in a first optical path. The at least one lens is positioned between the prism and the imager in a second optical path, where the second optical path is different from the first optical path. An image of the free air ball disposed at a lower portion of the wire bonding tool is provided to the imager via the prism and the at least one lens.
According to another exemplary embodiment of the present invention, a method for measuring a size of a free air ball for use with a wire bonder having a wire bonding tool and an Electric Flame Off (EFO) device is provided. The method includes receiving an indirect image of the free air ball via a prism, processing the received image of the free air ball to measure at least one dimension of the free air ball, and providing a control signal to the EFO device based on the at least one dimension of the free air ball.
According to yet another exemplary embodiment of the present invention, a method for analyzing an image of a free air ball for use with a wire bonder having an Electric Flame Off (EFO) device is provided. The method includes providing an image of the free air ball to an image processor during a wire bonding process, determining whether a characteristic of the free air ball is within a predetermined tolerance, and controlling at least one setting of the EFO system based on the determination step.
These and other aspects of the invention are set forth below with reference to the drawings and the description of exemplary embodiments of the invention.
The invention is best understood from the following detailed description when read in connection with the accompanying drawings. It is emphasized that, according to common practice, the various features of the drawings are not to scale. On the contrary, the dimensions of the various features are arbitrarily expanded or reduced for clarity. Included in the drawings are the following Figures:
The entire disclosure of U.S. patent application Ser. No. 10/458,535 filed on Jun. 6, 2003 and U.S. patent application Ser. No. 09/912,024 filed on Jul. 24, 2001 are expressly incorporated by reference herein, as if set forth in full.
According to certain exemplary embodiments, the present invention relates to a method and apparatus for measuring the size of a free air ball on the optical system of a wire bonder along with an optical cornercube prism based technology to image the capillary tip.
According to certain exemplary embodiments thereof, the present invention uses the optical system of a wire bonder and a cornercube based offset tool to image the free air ball disposed adjacent to or seated in the wire bonder capillary. The image is then analyzed to measure the ball size. To improve the accuracy of the ball measurement, an illumination system appropriate for producing a desirable image (e.g., high magnification image) is utilized. The optical system may be selected to produce the desired image (e.g., a low magnification image, a high magnification image, or any appropriate resolution, etc.) based on a number of factors including, for example, the size of the free air ball and other processing constraints. The system measures the diameter of a ball during normal operation of a wire bonder. The information is used to control the ball size via the EFO ball formation mechanism commonly found on wire bonders. The purpose of the system is to measure free air ball diameter in an effort to regulate the ball size for ultra fine pitch applications. The wire bonder then uses these values to determine and adjust settings for the EFO system.
According to another exemplary aspect of the invention, the ball size determination and control is a closed loop process. The wire bonder periodically measures the ball diameter and provides this information to the wire bonder so that the EFO system may produce the desired ball size continuously. This allows the free air ball size to be controlled during bonding operations, therefore correcting for any disturbances which would cause a free air ball to exceed its desired diameter tolerance during a wire bonding operation.
Currently, no apparatus or method exists on the wire bonder for measuring free air balls. According to certain exemplary embodiments thereof, the present invention allows the free air ball size to be controlled in a closed loop manner and therefore correct for any disturbances which would cause the free air ball to exceed its desired diameter tolerance during wire bonding operation.
The present invention allows the wire bonder to periodically measure the ball diameter and provide this information to the wire bonder so that the EFO system may produce the desired size ball continuously. A machine vision system may be used to analyze the image and measure the ball diameter. The present invention uses this information to control the ball size via the EFO ball formation mechanism commonly found on wire bonders today.
In an exemplary embodiment, cornercube offset alignment tool 109 (comprising cornercube 106 and lens elements 108, 110), has a total of three internal reflection surfaces, 218, 220, and 221 (best shown in
Optical imaging unit 102, such as a CCD imager, CMOS imager or a camera, for example, is mounted above image plane 112B in order to receive an indirect image of bonding tool 104 through cornercube offset alignment tool 109 (image plane 112B, shown in
In an exemplary embodiment, the focal point of the vision system (coincident with imaginary plane 211 shown in
The image plane of cornercube offset tool 109, including lens elements 108, 110, is coincident with the object plane 112B of optical imaging unit 102. In other words, the image plane of cornercube 106 and lens elements 108, 110 are aligned to bonding tool 104 which also lies in object plane 112A. In an exemplary embodiment, lens elements 108, 110 (or 205) preferably have a unitary magnification factor. First lens element 108 is positioned in a first optical axis 114 between bonding tool 104 and cornercube 106. Second lens element 110 is substantially in the same plane as that of first lens element 108 and is positioned in a second optical axis 116 between optical imaging unit 102 and cornercube 106 (see
The reference position of bonding tool 104 is shown as a reflected ray which travels from first position 202 along first optical axis 114 (shown in
Consider now that the position of bonding tool 104 is displaced by a distance 222 due to a variation in system temperature, for example. As shown in
As illustrated, the original displacement of bonding tool 104, shown as offset position 222, is evidenced by the difference 224 in the measured location of bonding tool 104 at second position 208 with respect to reference location 204. As evidenced by the above illustration, a positional shift in assembly 109 does not affect the reflected image as viewed by imaging unit 102. In other words, assembly 109 of the present invention may be translated along one or both the X and Y axes such that the image of the bonding tool 104 appears relatively stationary to imaging unit 102. There will be some minimal degree of error, however, in the measured position of bonding tool 104 due to distortion in the lens system (discussed in detail below).
Referring again to
Exemplary cornercube 106 comprises top surface 226, first reflective surface 218, bottom surface 223, second reflective surface 220, and third reflective surface 221. If top surface 226 is set such that optical axes 114, 116 are normal to top surface 226, first reflective surface 218 will have a first angle 230 of about 45° relative to top surface 226, and a second angle 234 of about 135° relative to bottom surface 223. Likewise, ridgeline 225 (formed by the intersection of second and third reflective surfaces 220 and 221) has similar angles 232 and 236 relative to top surface 226 and bottom surface 223, respectively. In addition, second and third reflective surfaces 220 and 221 are orthogonal to one another along ridgeline 225. In the exemplary embodiment, bottom surface 223 of cornercube 106 may be used as a mounting surface if desired. It should be noted, however, that it is not necessary to form top surface 226 so that the image and reflected rays are normal thereto. As such, cornercube 106 will redirect the incident light or transmit image of bonding tool 104 parallel to itself with an offset equal to 118.
The present invention can be used with light, for example, in the visible, UV and IR spectrum, and preferably with light having a wavelength that exhibits total internal reflection based on the material from which cornercube 106 is fabricated. The material selected to fabricate cornercube offset alignment tool 109 is based on the desired wavelength of light which the tool will pass. It is contemplated that cornercube offset alignment tool 109 may be fabricated to handle a predetermined range of light wavelengths between the UV (1 nm) to the near IR (3000 nm). In a preferred embodiment, the range of wavelength of light may be selected from between about i) 1 and 400 nm, ii) 630 and 690 nm, and iii) 750 and 3000 nm. Illumination may also be provided by ambient light or by the use of an artificial light source (not shown). In one exemplary embodiment, typical optical glass, having an index of refraction of 1.5 to 1.7, may be used to fabricate cornercube 106. Note, the index of refraction is based upon the material chosen for maximum transmission at the desired operating wavelength. In one embodiment, cornercube offset alignment tool 109 has an index of refraction of about 1.517.
As shown in
As shown in
In use, free air ball 1415 is formed by an EFO system (not shown) at a lower portion of capillary 1404. Imager 1402 is able to view free air ball 1415 (from object plane 1412) as an image formed at image plane 1410 via lens 108, cornercube offset tool 106 and lens 110.
The image of a free air ball 1415 is provided by optical imager 1402 to an image processing system (not shown in this figure) where dimensions, such as the diameter, of free air ball 1415 is determined. Based on this determination the parameters of the EFO system may be adjusted in a closed loop feed-back arrangement, as necessary, to control the diameter of further free air balls to continuously ensure proper bonding. Thus, the inventive controlled closed loop system may correct for anomalies which would otherwise cause free air ball 1415 to exceed its desired diameter tolerance or to have a diameter too small during the wire bonding operation.
As mentioned above, this variation of the first exemplary embodiment accommodates various die sizes which these types of equipment accept and place. In this exemplary embodiment, down looking optical detector 1002, such as a camera, (e.g., a substrate camera) views features on the downward side of the component to be placed, such as die, 1008, 1010, or 1012. These features of die 1008, 1010, 1012, can then be identified via a vision system (not shown) to accurately place the die on the substrate (not shown) using pick tool 1004 based in part on the predetermined distance 1006 between pick/place tool 1004 and optical detector 1002. It is understood by those of skill in the art, that pick tool 1004 may be either a rotating or non-rotating pick tool. This exemplary embodiment further preserves the optical advantages with respect to accuracy of the cornercube alignment described above in the first exemplary embodiment.
Lenses 1016, 1018, 1022, 1024, 1028, 1030 may be formed from a unitary optical member rather than individual lenses if desired to simplify assembly of the system. Such an approach is shown in
Next, and as shown in
As shown in
Once the first sub-fiber is aligned with single fiber 1208, the process is repeated for a further sub-fiber, such as 1202 b, and another single fiber (not shown).
Of course the exemplary embodiment is not limited to the fiber optic bundle of a fiber optic splitter being below optical detector 1002. The embodiment also contemplates that the relative positions of fiber optic bundle 1200 and optical fiber 1208 are reversed, such that fiber optic bundle 1200 is positioned above cornercube prism 1014.
Next, and as shown in
Although the present invention has primarily been illustrated and described with respect to a cornercube device (e.g., a cornercube prism) it is not limited thereto. Other prism devices may be used, particularly other reflective prisms. In certain configurations of the present invention, it is desirable to have parallel image rays. In such a configuration, a reflective prism such as a cornercube prism may provide a beam which enters and exits the prism substantially parallel to one another; however, in certain configurations non-parallel beams/image rays may be desired, and other types of prisms may be utilized.
Although the present invention has primarily been described in relation to apparatuses and methods for measuring the size of a free air ball, it is not limited thereto. The apparatuses and methods disclosed herein are useful for measuring a shape of a free air ball, a texture of a free air ball, and any other quality of a free air ball that may be determined using the disclosed techniques. For example, such shapes and textures of free air balls may be compared to a threshold shape or texture to further control the free air ball formation process (e.g., a closed loop process).
Although the invention has been described with reference to exemplary embodiments, it is not limited thereto. Rather, the appended claims should be construed to include other variants and embodiments of the invention, which may be made by those skilled in the art without departing from the true spirit and scope of the present invention.
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|U.S. Classification||228/4.5, 353/81, 228/9, 356/127, 228/104, 228/102, 228/180.5, 359/431|
|International Classification||B23K20/10, B23K37/00, B23K31/02, G01B11/00, B23K31/12, B23K20/00|
|Cooperative Classification||B23K2201/40, B23K31/12, B23K20/007, B23K20/10, H01L2924/14, H01L2224/78301|
|European Classification||B23K20/00D2B2, B23K20/10, B23K31/12|
|Sep 7, 2005||AS||Assignment|
Owner name: KULICKE AND SOFFA INDUSTRIES, INC., PENNSYLVANIA
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNORS:BEATSON, DAVID T;SOOD, DEEPAK;LUCAS, NORMAN;AND OTHERS;REEL/FRAME:016499/0718;SIGNING DATES FROM 20050805 TO 20050816
|Oct 29, 2012||FPAY||Fee payment|
Year of fee payment: 4